Summary of chemistry doctoral thesis: Study on synthesis, characteristics, and adsorption properties of toxic organic substances in the water environment of mesoporous carbon materials

The thesis has found a new method to increase the pore size of mesoporous carbon by filling the liquid glass into the pore of the template (silica SBA-15) before impregnating the carbon presource to limit the penetration of carbon sealed the pore system of SBA-15. Stability of mesoporous carbon is increases due to silicon are partially retained in materials. This technique opens the way of synthesis of mesoporous carbon as an adsorbent with a desired pore size and stability.

MINISTRY OF EDUCATION

AND TRAINING

VIETNAM ACADEMY OF SCIENCE AND TECHNOLOGY

GRADUATE UNIVERSITY OF SCIENCE AND

TECHNOLOGY -

NGUYEN THI HONG HOA

STUDY ON SYNTHESIS, CHARACTERISTICS AND ADSORPTION PROPERTIES OF TOXIC ORGANIC SUBSTANCES IN THE WATER ENVIRONMENT OF MESOPOROUS CARBON MATERIALS

Major: Theoretical Chemistry and Physical Chemistry Code : 62.44.01.19

SUMMARY OF CHEMISTRY DOCTORAL THESIS

Ha Noi – 2019

The work was completed at: Graduate Universty of Science and Technology - Vietnam Academy of Science and Technology

Science supervisor 1: Assoc.Prof.Dr Dang Tuyet Phuong

Science supervisor 2: Dr Tran Thi Kim Hoa

Thesis can be found at:

- Library of the Graduate University Science and Technology

INTRODUCTION

1 The necessity of the thesis

Mesoporous carbon materials have an ordered structure, uniform pore size They often were synthesized by two methods: soft-templating and hard-templating With the soft-templating method, materials have been prepared via self-assembly by using soft-templating (surfactant) The obtained materials have less orderly structure The pore size of the material is difficult to control and the template is difficult to remove With the hard-templating method, MCM-48, SBA-15, etc are used as the templates The materials have highly order structure, uniform and easily controlled pore size Therefore, hard-templating method is used more widely However, the pore size of materials is smaller than that of the hard-templates because obtained materials are inverse copies of the templates The thickness of the wall and the pore size are limited by size and shape form of hard-templates So far, the pore size of mesoporous

carbon materials are synthesized by hard-templating method only

reach the maximum of ~ 5.5 nm The increasing in pore size is not feasible because it is limited by the size of the templates, resulting in framework collapse and pore breakage due to decrease stability Hence, it is necessary to find new methods to synthesize mesoporous carbon materials with larger sizes, higher stability

Mesoporous carbon materials are said to be a good adsorbent

of organic substances in water environment However, these materials are not stability The structure of the materials is easily broken during the reuse process and it is difficult to recover So, the regeneration and reuse of mesoporous carbon materials are very difficult Because of, if heat is used to remove completely adsorbed,

it is necessary to perform high temperature causing to burn mesoporous carbon materials Also, the solvents are used to remove the adsorbed, resulting less-economical effect and secondary pollution Therefore, the research to find the effective and feasible methods for regeneration and reuse of mesoporous carbon materials

is necessary

From the above reasons, the thesis topic “Study on synthesis, characteristics, and adsorption properties of toxic organic substances in the water environment of mesoporous carbon materials” was studied

2 The purpose of the thesis

Study on control the process of synthesizing mesoporous carbon materials with an ordered structure, large pore size, high stability They are as an effective adsorbent for toxic organic substances with different molecular sizes in water environment

Synthesis of mesoporous carbon materials with desired order structure, large pore size, high durability for effective adsorption of different molecular size toxic organic substances in water environment

3 Scientific and practical significance of the thesis

The thesis has found a new method to increase the pore size

of mesoporous carbon by filling the liquid glass into the pore of the template (silica SBA-15) before impregnating the carbon presource

to limit the penetration of carbon sealed the pore system of SBA-15 Stability of mesoporous carbon is increases due to silicon are partially retained in materials This technique opens the way of synthesis of mesoporous carbon as an adsorbent with a desired pore size and stability

Doping iron into the framework of mesoporous carbon materials creates catalysts to decompose adsorbed, release the adsorption sites, regeneration and reuse of mesoporous carbon, extend the scope of application of materials for treatment of toxic organic substances in water

4 New findings of the thesis

1 For the first time, a new technique is used to control the

pore size of the mesoporous carbon materials which is synthesized

by hard – temlating method by filling the liquid glass into the pore of SBA-15 before impregnating the carbon source to prevent penetration carbon to seal the pore system of SBA-15 This technique opens new direction for mesoporous carbon synthesis technologies as the adsorbent with the desired pore size

2 Retaining a silicon part in synthesiszed material to increase the stability of the mesoporous carbon material

3 Using atom-planting method to put iron into framework of

the mesoporous carbon material do not change the structure of the

materials Iron exists on the surface of materials in the highly dispersed Fe2O3 and FeO forms, favorable for adsorption and decomposition of methylene blue, enhance the ability of regeneration, reuse and do not cause secondary pollution

5 The structure of the thesis

The thesis consists of 140 pages with 83 figures, 31 tables The thesis includes the following sections: Introduction (2 pages); Chapter 1: Overview (44 pages); Chapter 2: Research methods and experiment (16 pages); Chapter 3: Results and discussion (59 pages); Conclusions(2 pages); Novel scientific contributions of the thesis;

List of publications; References and appendices

CHAPTER 1 OVERVIEW

Chapter 1 includes a general introduction of synthesis methods, application of mesoporous carbon materials and metal containing mesoporous carbon Mesoporous carbon materials are synthesized by two methods: soft-templating and hard-templating Metal containing mesoporous carbon materials are synthesized by two methods: impregnation and atom-planting In this chapter, adsorption properties, application and adsorption mechanism of mesoporous carbon materials in the field of adsorption were introduced

CHAPTER 2 RESEARCH METHODS AND EXPERIMENT 2.1 Chemistry

- F127 (Sigma-Aldrich); Phenol (China); Focmaldehit (China);

SBA-15, MCF (Synthesis from liquid glass - Department of Surface Chemistry - Institute of Chemistry - Vietnam Academy of Science and Technology); Refined sugar (Vietnam); Liquid glass (Vietnam)

Figure 2.3 Process of synthesizing mesoporous carbon

The CMQTBC(TTL) pattern is synthesized using a hard-templating method, but the liquid glass is filled into the pore of SBA-15 before impregnating the carbon source

Table 2.2 Samples of mesoporous carbon

1

T ( o C)

2 N1 Templating

3

N2 CMQTBM1

templating

1 Temperature; 2 Number of impregnation; 3 Number of g Na 2 SiO 3

2.2.2 Synthesis of iron containing mesoporous carbon

- Synthesis of Fe-t-CMQTBC(TTL) by impregnating iron nitrate 0.2

Langmuir, Freundlich adsorption isotherm models

The pseudo-fisrt-order and pseudo-second-order adsorption kinetic models

2.6 Method of evaluating the ability to reuse materials

Recover the material after adsorption and wash with water and ethanol + methanol (methanol and ethanol 1: 2 ratio, V = 60 ml) stir for 2 hours at 60 ° C Then, the material is used to adsorb MB

CHAPTER 3 RESULTS AND DISCUSSION

3.1 Synthesis of mesoporous carbon

3.1.1 Soft-templating method

*) Effect of temperature 80 o C, 100 o C, 120 o C:

Figure 3.1; 3.2 XRD patterns (A) and nitrogen

adsorption-desorption isotherms (B) of mesoporous carbon are synthesized at different temperatures

Temperature increase → Brown motion increases → assembly of surfactants increase → The length of the hydrophobic chain increases → pore size increases Temperature high (over 100

Self-oC) → evaporate water, flocculate surfactants → pore size decreases

So, the optimal synthetic temperature is 100 oC

*) Effect of pH = 1, 2, 3:

Figure 3.5; 3.6 XRD patterns (A) and Nitrogen

adsorption-desorption isotherms (B) of CMQTBM1, CMQTBM2 and CMQTBM3

The zero charge point of silicon is 2, if pH = 2, mesoporous carbon materials are formed according to the correct mechanism

S0H+X− I (S: F127, X− Cl−; I: Si)

Thus, conditions of suitable syntheting of materials are at

100 °C and pH = 2, the obtained materials have a mesoporous structure with pore size of 5.4 nm, surface area BET of 1693 m2/g

3.1.2 Hard-templating method

3.1.2.1 Templating: using two templating with the same hexagonal

structure, but the pore size of MCF is larger than that of SBA-15

Figure 3.9; 3.10 XRD patterns of SBA-15; CMQTBC(SBA-15) (A)

and MCF; CMQTBC(MCF) (B)

XRD pattern shows that the structure of CMQTBC(SBA-15) and CMQTBC(MCF) is similar to that of SBA-15 and MCF

Figure 3.11 TEM

CMQTBC(SBA-15) and CMQTBC(MCF)

The structure of CMQTBC(SBA-15) and CMQTBC(MCF) samples have a hexagonal structure and uniform pore size (Figure 3.11 and 3.12) The pore size of CMQTBC(MCF) is larger than that

of CMQTBC(SBA-15) because of the pore size of MCF is larger than that of SBA-15

Figure 3.12 Nitrogen

adsorption-desorption isotherms 15) and CMQTBC(MCF)

Figure 3.12 shows that both

CMQTBC(MCF) belong to type IV isotherm with a hysteresis The pore sizes of CMQTBC(SBA-15) and CMQTBC(MCF) are in the range

of respectively 4.2 nm; 5.6 nm

Figure 3.13 TGA patterns of CMQTBC(SBA-15) (A) and

CMQTBC(MCF) (B)

TGA data show that CMQTBC(SBA-15) (complete combustion temperature of 595 oC) has higher thermal stability than CMQTBC(MCF) (552 oC) does Therefore, SBA-15 is selected as templating to synthesize mesoporous carbon materials

3.1.2.2 Amount (number of impregnation) of carbon source

Figure 3.15 Nitrogen

adsorption-desorption isotherms (A) and pore size distributions (B) of SBA-15,

CMQTBC1(SBA-15), CMQTBC2(SBA-15) and CMQTBC3(SBA- 15)

Figure 3.15A shows that all four samples SBA-15, CMQTBC1(SBA-15), CMQTBC2(SBA-15) and CMQTBC3(SBA-15) belong to type IV isotherm with a hysteresis which are typical for

mesoporous materials Figure 3.15B shows that the pore distribution

of CMQTBC2(SBA-15) is the narrowest with the pore size concentrated mainly in the 4-5 nm range Thus, the most number of impregnated carbon precursor is 2

3.1.2.3 Controlling pore size

We use silicon from liquid glass to fill the pore of SBA-15 before impregnating the carbon precursor and prevent carbon from penetrating into the pore Then the silicon is removed by HF and the obtained mesoporous carbon materials have the pore system larger than that of the initial SBA-15 (Figure 3.19)

Figure 3.19 Simulate the synthesis process of CMQTBC(TTL)

Figure 3.16 XRD pattern of CMQTBC(TTL)

Figure 3.16 shows that CMQTBC(TTL) has a peak at very low scanning angle (below 0.5o), outside the detection threshold of the meter Due to the small angle θ, a large distance d can be predicted, leading

to large pore size

Figure 3.17 Nitrogen adsorption-desorption isotherms (A) and pore size distributions (B) of SBA-15, CMQTBC(SBA-15) and CMQTBC(TTL)

Figure 3.18 TEM images of

CMQTBC(SBA-15) (A) and CMQTBC(TTL) (B)

Figure 3.17 and 3.18 show that CMQTBC (TTL) has a large pore size (10.4 nm), fairly uniform pore This result is consistent with the XRD analysis data

The synthesis process consists of stages (Figure 3.19): Stage 1: mixing liquid glass and SBA-15 templating obtain SBA-15(TTL) with pore of SBA-15 filled by liquid glass Stage 2: impregnating carbon precursor onto SBA-15(TTL) and carbonization obtained C-SiO2 material Stage 3: C-SiO2 is washed with HF 10% for the first time to obtain C3 material Stage 4: C3 is washed with HF 10% for the second time to obtain CMQTBC(TTL) material Stage 5: washing CMQTBC(TTL) with HF 10% 3 times obtain C5 material

Table 3.6 The characteristic parameter for porous properties of

SBA-15(TTL), C-SiO 2 , C3 (washing HF 1 st ), CMQTBC(TTL)

From table 3.6 shows CMQTBC(TTL), is washed 2 times by

HF, has a surface area SBET (772 m2/g) and a porosity Vpore (1,698

cm3/g) higher than material is no washing or washing 1 time After the 3rd washing (C5 sample), Si is completely removed, the surface

area SBET and porosity Vpore increase to 1276 cm3/g and 4.304 cm3/g respectively because silicon was further removed, causing the expanding of pore, increasing in the average pore volume but the structure is less stable and the signs of structural collapse occur (Figure 3.21)

Figure 3.21 SEM images of

XPS spectra (Figure 3.24) show the peaks at the energy level

of 103 eV; 285 eV; 530 eV which are assigned to the presence of Si2p; C1s, O1s in CMQTBC(TTL) materials

Thus, with the technique of using pore-filled liquid glass SBA-15, synthesized MC material with large pore size (10.4 nm), surface area (772 m2/g) and high pore volume (1.603 cm3/g)

Sumary:

For soft-templating method: conditions of suitable synthetic materials are at 100 o C, pH = 2 The obtained materials have a

mesoporous structure with a pore size of 5.4 nm, porous characteristics, and BET surface area of 1693 m 2 /g The order of materials is not high

For hard-templating method:

- Suitable conditions for synthesizing materials: SBA-15 is template and number of impregnation is 2;

- It is possible to change the pore size of materials by using different templates with different pore sizes such as SBA-15 and MCF

- filling the liquid glass into the pore of SBA-15 before impregnating the carbon source to prevent penetration carbon to seal the pore system of SBA-15 resulting the adsorbent with the desired pore size.is a new technique that has never been reported in the literature

- Stability of the mesoporous carbon materials increases due

to retaining a part of silicon in the material

3.2 Synthesis of iron containing mesoporous carbon

XRD patterns (Figure 3.25) show that the structure of CMQTBC(TTL) and Fe-b-CMQTBC(TTL) is similar to that of CMQTBC(TTL) (Figure 3.16), demonstrating that doping iron into the material does not affect the structure of the material

Fe-t-Figure 3.26 shows that Fe-t-CMQTBC(TTL) material does not have characteristic peak for iron on the material, may be small iron content below the detection threshold of XRD method or exists amorphous form Fe-b-CMQTBC(TTL) has peaks with a value of 2θ

in accordance with the standard data for the structure of Fe2O3 This shows that with the atomic implant method, iron exists the form of oxide on mesoporous carbon

TEM images (Figure 3.27) show that the doping Fe does not

change the structure of mesoporous carbon material and highly

disperses iron

Figure 3.28 FTIR spectra of

CMQTBC(TTL), CMQTBC(TTL) and Fe-t- CMQTBC(TTL)

Fe-t-FTIR spectra (Figure 3.28) show the existence of –OH, C–H, -C=C, -C=O, and -C–O groups in structure of CMQTBC(TTL), Fe-t-CMQTBC(TTL) and Fe-b-CMQTBC(TTL) With iron containing samples (Fe-t-CMQTBC(TTL) and Fe-b-CMQTBC(TTL)) have additional peaks at 457.13 và 435.91 cm-1 assigned to peak of the link Fe–O